This invention relates to a developing apparatus and a method for manufacturing a developer support and more particularly to a developing apparatus used with a copier or printer using electrophotographic technology and a method for manufacturing a developer support used with the developing apparatus.
With a copier or printer using electrophotographic technology, an electrostatic latent image is formed using photoconductive material and a charged developer is attracted to the electrostatic latent image for making it visible by developing. A cylindrical developer support is used to supply the developer to be attracted. At such developing apparatus, the supply amount of the developer to the electrostatic latent image must be an amount responsive to the charge potential of the electrostatic latent image. However, when a developer comprising particles or being high in charge performance is used, a developing capability distribution occurs in the developer on the developer support due to a developing history and supplying the developer in response to the charge potential may not be performed. This phenomenon is called a ghost, the cause of which can be described qualitatively as follows:
FIG. 4 shows an outline of the configuration of a developing apparatus using a magnetic developer. The developing apparatus comprises a developer support 11, a magnet 12, a developer hopper 13, and a developing blade 14. A developer 15 is stored in the developer hopper 13. The developer is attracted to the developer support 11 by a magnetic force of the magnet 12. As the developer support 11 rotates, the developer that adheres on the developer support is controlled to a predetermined film thickness by means of the developing blade 14. The developer is charged due to friction of the developer components against each other or friction of the developer against the developing blade. The charged developer is transferred to an electrostatic latent image on an electrostatic latent image holder 16 by a Coulomb force at a place near the electrostatic latent image holder, making the electrostatic latent image visible by developing. When the electrostatic latent image is made visible by developing, only the part of the developer on the developer support 11 positioned in the portion corresponding to the electrostatic latent image is consumed. As the developer support rotates, a new developer part is supplied to the consumed part and charged by means of the developing blade 14.
Since development is performed by such operation, the new developer part supplied to the developer consumption portion at the developing step is charged only once due to friction by means of the developing blade, but any other part, namely, old part is again charged due to friction. Thus, the developer on the developer support 11 has a charge amount distribution responsive to a developing history. As the charge amount increases, Coulomb interaction between the developer and electrostatic latent image becomes strong and at the same time, attraction by a mirror imaging force also becomes strong between the developer and developer support. The transfer amount of the developer to the electrostatic latent image, namely, the developing capability is determined by the strength relationships among the forces. Thus, in the actual developing, the developing capability of the portion to which a new developer part is supplied may be high or low as compared with any other portion and an image different from the electrostatic latent image will appear on the print result accordingly.
For example, consider making a copy of a manuscript having a portion written as "GHOST" and a shaded area at a unique density, as shown in FIG. 5. Usually, the peripheral speed of the developer support 11 is fast as compared with that of the electrostatic latent image 16, but for convenience, assume that the former equals the latter. Also, assume that developing is performed from top to bottom in FIG. 5.
Since the length of the circumference of the developer support generally is shorter than the length of a manuscript, the developer support needs to rotate more than once to copy one sheet of manuscript. Assume that the length indicated by L in FIG. 5 is the length of the circumference of the developer support. By developing the portion, a developer layer having a developing capability distribution responsive to the electrostatic latent image, namely, a ghost is formed on the surface of the developer support, and the next portion is developed with the layer. At the time, if the developing capability of the developer part used for developing the characters is high as compared with any other developer part, an image not contained in the electrostatic latent image, called a positive ghost, appears on the developing result at the position responsive to the length of the circumference of the developer support, L, as shown in FIG. 6. In contrast, if the developing capability of the part is low, the electrostatic latent image exists, but is not developed, that is, a phenomenon called a negative ghost occurs.
The phenomenon relates to the charge performance of a developer as described above, thus becomes obvious particularly when a developer comprising particles or improved in charge performance developed to provide a high picture quality in recent years is used.
Techniques disclosed in Japanese Patent Laid-Open Nos.Hei 1-276174 and 1-277265 are known as techniques to cope with the ghost. In the techniques, a resin layer having conductivity and a surface lubricating ability consisting of phenol resin and carbon is formed on the developer support surface, thereby suppressing occurrence of a ghost.
However, the process wherein the resin layer is formed on the developer support surface has problems of complicated forming process of the resin layer, easy peeling-off of the resin layer because of weak adhesive strength of the resin layer and substrate, and a short term in which the ghost can be suppressed.